Martensite TiAl alloy and preparation method thereof

Abstract

The invention discloses a martensite TiAl alloy which comprises the following components in percentage by atom: 38-43% of Al, 6.5-8.5% of V and 0.1-2% of Zr, and the total atomic percentage of V and Zr is 8.5. In addition, the invention further discloses a method for preparing the martensite TiAl alloy, and the method comprises the following steps: uniformly mixing target components of sponge titanium, high-purity aluminum particles, high-purity vanadium particles and high-purity zirconium particles in proportion to prepare a casting material to be used; the casting materials in the first step are repeatedly smelted for multiple times through a vacuum electric arc smelting furnace, and cast ingots with uniform components are obtained; cutting a sample to be subjected to heat treatment from the central part of the cast ingot; and placing the sample to be subjected to heat treatment in a heat treatment furnace at 1400 DEG C, preserving heat for 20 minutes, taking out, and quenching with water. The martensite TiAl alloy is prone to martensite transformation, the structure of the martensite TiAl alloy contains a high amount of martensite, and the martensite TiAl alloy has wide application prospects.

Description

Technical Field

[0001] The present disclosure generally relates to a martensitic TiAl alloy and a method for preparing the same. Background Art

[0002] TiAl alloys offer a range of advantages, including low density, high specific strength, high specific stiffness, good oxidation resistance, and excellent high-temperature creep properties, and hold broad application prospects in the aerospace field. However, the practical application of this material faces two key challenges: first, insufficient room-temperature plasticity, which makes it difficult to form (elongation is generally less than 2%); and second, coarse, fully lamellar structures (typically >200 μm) are prone to crack initiation along lamellar interfaces under cyclic loading, resulting in a sharp reduction in service life.

[0003] In view of this, optimization of alloy composition and heat treatment process has become an important aspect of studying the performance improvement of TiAl alloys.

[0004] For example, patent CN110512116A discloses a new high-Nb-TiAl alloy material for additive manufacturing, with an intermetallic compound content of 40-50% Al, 4-12% Nb, 0-15% (W, Ta, Mo, Co), 0-4.5% (Ni, Fe, Hf, Zr), 0-4% (V, Cr, Mn), 0-2% B, 0-3% (C, Si), and 0-3% rare earth elements, with the number of alloying elements being no less than six. However, this alloy is specifically designed for additive manufacturing and has a higher production cost than casting. Moreover, if used as a casting alloy component, it faces difficulties in precise control due to the large number of added elements, and is prone to problems such as element volatilization, accumulation in certain parts, and shrinkage and shrinkage cavities.

[0005] Patent CN103924121A discloses a titanium-aluminum-based alloy for casting and its preparation method, belonging to the field of γ-TiAl-based intermetallic compound alloy materials. The alloy comprises, by atomic percentage, the following: Ti-(46.0-48.0)Al-(1.5-3.5)V-(0.5-1.5)Cr-(0.1-0.5)M, where M is one or both of Zr and Hf, and the remainder are impurity elements. Furthermore, by atomic percentage, (0.1-0.5)C may be added. By adding trace amounts of solid solution strengthening elements Zr and / or Hf and dispersion strengthening phase-forming element C, the alloy significantly improves the alloy's high-temperature strength, creep resistance, and structural stability while maintaining a room temperature tensile plasticity of more than 2.0%, thereby improving the high-temperature service performance of the cast titanium-aluminum-based alloy and increasing the original alloy's operating temperature from 750°C to 850°C. However, whether this alloy can achieve its advertised properties remains to be seen. Like the above alloys, it also faces the problem of difficulty in precise control due to the large number of added elements, and is prone to problems such as element volatilization, aggregation in certain parts, shrinkage and cavitation.

[0006] None of the above prior art methods mentions the concept of using martensitic transformation to refine the microstructure of TiAl alloys, in which the β decomposition mechanism changes from block to martensite after β phase field water quenching in the Ti-Al alloy system. Summary of the Invention

[0007] In view of this, the inventors of the present invention proposed to expand the β single-phase region by adding β-stabilizing elements and reducing the Al content, so that the alloy can undergo martensitic transformation at a relatively low temperature to obtain martensite. As a result, the TiAl alloy passes through the β phase region (L→L+β→β→β+α→α) during solidification, thereby avoiding the peritectic reaction (L+β→α) and obtaining a finer structure.

[0008] Specifically, for TiAl alloys, Fe, W, V, Nb, Mo, and Cr are β-phase stabilizing elements. Fe, Cr, and V are relatively strong β-stabilizing elements, with Fe being the strongest β-phase stabilizing element, followed by Cr, and then V. Nb has the weakest ability to stabilize the β-phase among these elements. Compared to Nb, V can significantly improve the room temperature tensile strength. Considering the comprehensive performance, this study selected V rather than Fe, Cr, or Nb as the main additive element. Regarding the Al content, in order for β-phase solidification to occur, the Al content needs to be ≤45 at.%. Excessive content will produce B2 phase at room temperature, making the TiAl alloy hard and brittle. At the same time, considering that the present invention focuses on high-temperature TiAl alloys, the Al content should not be too low, so an Al atomic percentage content of 38 to 43 is selected.

[0009] In addition to the significant β-phase stabilizing elements, the art typically adds third components such as Hf, Zr, C, B, and Y to refine the grains, which can improve the high-temperature mechanical strength of TiAl alloys. Among them, B is the most commonly used microstructure-refining element, and its refining effect is recognized in the industry. Currently, it is far more widely used than Zr. The inventors of the present invention are particularly aware that Zr, as a congener of Ti, can replace a large number of Ti atoms in the alloy. In view of this, the inventors of the present invention proposed using Zr rather than B to achieve solid solution strengthening of TiAl alloys. The present invention has indeed verified that compounds formed by Zr have the effect of hindering dislocation slip and suppressing crack propagation, refining the grains, and being relatively beneficial to the mechanical properties of the alloy. In addition, although C is also a grain-refining additive element in TiAl alloys, the inventors of the present invention took into account the complex phase transformation of TiAl alloys and the different solid solubility of C in the γ phase and α2 phase. C atoms mainly occupy interstitial positions in TiAl alloys, and carbides will only precipitate when the content exceeds its solid solubility limit. Moreover, similar to borides, the precipitation of carbides is also affected by the heat treatment process. In summary, the inventors of the present invention chose to add V and Zr elements and abandoned B and C elements.

[0010] At the same time, considering that there is also research on martensitic phase transformation in TiAl alloys in the prior art, but the degree of transformation to martensite in TiAl alloys prepared by the prior art is very small, the inventors of the present invention specifically add V and Zr elements to TiAl alloys at the same time to form a large amount of martensite.

[0011] According to one aspect of the present invention, a martensitic TiAl alloy is provided, wherein the martensite content is at least 80%, more preferably the martensite content is at least 85%, particularly preferably the martensite content is at least 90%, and even more preferably the martensite content is at least 95%. The TiAl alloy contains, in atomic percentage (at.%), 38-43% Al, 6.5-8.5% V, 0.1-2% Zr, and the balance is Ti and unavoidable impurities, with the total atomic percentage of V and Zr being 8.5.

[0012] According to one embodiment of the present invention, the martensitic TiAl alloy contains, in atomic percentage, 40-42% Al, 6.5-8.5% V, 0.1-2% Zr, and the balance being Ti and unavoidable impurities.

[0013] According to one embodiment of the present invention, the TiAl alloy contains, in atomic percentage, 42% Al, 6.5% V, 2% Zr, and the balance being Ti and unavoidable impurities.

[0014] According to one embodiment of the present invention, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1350-1450° C., keeping the ingot warm for 10-30 minutes, and then taking it out and quenching it with water.

[0015] According to one embodiment of the present invention, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1380-1450° C., keeping the ingot warm for 20-30 minutes, and then taking it out and quenching it with water.

[0016] According to one embodiment of the present invention, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400-1450° C., keeping the ingot warm for 20-30 minutes, then taking it out and quenching it with water.

[0017] According to one embodiment of the present invention, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400° C., keeping the ingot at the temperature for 20 minutes, and then taking it out and quenching it with water.

[0018] According to one aspect of the present invention, there is provided a method for preparing a martensitic TiAl alloy according to any one of the above items, characterized in that it comprises the following steps: Step 1: Ingredients The titanium sponge, high-purity aluminum particles, high-purity vanadium particles, and high-purity zirconium particles are uniformly mixed in the proportions described in any one of claims 1 to 3 to prepare a casting material to be used; Step 2: Melting ingots The casting material in step 1 is repeatedly melted multiple times in a vacuum arc melting furnace to obtain an ingot with uniform composition; Step 3: Cutting Cut the sample to be heat treated from the center of the ingot; Step 4: Heat treatment The sample to be heat-treated is placed in a heat treatment furnace at 1300-1450° C., kept warm for 10-30 minutes, and then taken out and quenched with water.

[0019] According to the method for preparing the martensitic TiAl alloy in one embodiment of the present invention, the TiAl alloy contains, in atomic percentage, 42% Al, 6.5% V, 2% Zr, and the balance being Ti and unavoidable impurities.

[0020] The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1350-1450° C., keeping the ingot warm for 10-30 minutes, taking the ingot out, and quenching the ingot with water.

[0021] According to the method for preparing the martensitic TiAl alloy according to one embodiment of the present invention, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1380-1450°C, holding the ingot at that temperature for 15-30 minutes, and then taking it out and quenching it with water. Further preferably, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400-1450°C, holding the ingot at that temperature for 20-30 minutes, and then taking it out and quenching it with water. Even further preferably, the martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400°C, holding the ingot at that temperature for 20 minutes, and then taking it out and quenching it with water.

[0022] Faced with the challenging conditions for martensite formation in TiAl alloys, the inventors of the present invention rationally adjusted the types and contents of β-stabilizing elements and appropriately reduced the Al content, thereby expanding the β single-phase region and making the TiAl alloy more susceptible to martensitic transformation, resulting in a high-martensite martensitic TiAl alloy. Furthermore, the use of Zr as a relatively neutral β-stabilizing element helps neutralize and increase the martensite content in the alloy, thereby avoiding the increased brittleness often associated with high V content in the martensitic TiAl alloy and reducing the alloy's brittleness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other purposes, features, and advantages of the present disclosure will become more apparent through a more detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings. The accompanying drawings are intended to provide a further understanding of the embodiments of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the present disclosure and are not intended to limit the present disclosure. In the drawings, the same reference numerals generally represent the same components or steps.

[0024] Figure 1 (a) and (b) respectively show the scanning electron microscope (BSE-SEM) microstructure and EBSD analysis results of the TiAl alloy after heat treatment according to Example 1 of the present disclosure, wherein the white matrix is ​​the B2 phase and the gray phase is the α2′ martensite phase.

[0025] Figure 2 The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment according to Example 2 of the present disclosure is shown, wherein the white matrix is ​​the B2 phase and the gray phase is the α2′ martensite phase.

[0026] Figure 3 The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment according to Example 3 of the present disclosure is shown, wherein the white matrix is ​​the B2 phase and the gray phase is the α2′ martensite phase.

[0027] Figure 4The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment in Comparative Example 1 of the present application is shown, wherein the white matrix is ​​the B2 phase and the gray phase is the α2 phase.

[0028] Figure 5 (a) and (b) respectively show the scanning electron microscope (BSE-SEM) microstructure and EBSD analysis results of the TiAl alloy after heat treatment in Comparative Example 2 of the present application, wherein the white matrix is ​​the B2 phase and the gray phase is the α2 phase.

[0029] Figure 6 (a) and (b) respectively show the scanning electron microscope (BSE-SEM) microstructure and EBSD analysis results of the TiAl alloy after heat treatment in Comparative Example 3 of the present application, wherein the white matrix is ​​the B2 phase and the gray phase is the α2 phase. DETAILED DESCRIPTION Example 1

[0030] This embodiment aims to provide a martensitic TiAl alloy, i.e., a TiAl alloy containing relatively more martensite in its microstructure, and a preparation method thereof. The designed composition is: Ti-42Al-6.5V-2Zr in terms of alloy atomic percentage, with the balance being Ti and unavoidable impurities.

[0031] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for the smelting and casting of ingots are titanium sponge (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio to prepare a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for potential element losses during smelting.

[0032] Step (2) Melting the ingot The raw materials from step 1 were melted into button ingots in a vacuum arc melting furnace (VAR). The melting process was repeated five times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled within the range of 0.2kA to 0.3kA.

[0033] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0034] Step (4) Heat treatment The block sample was placed in a crucible, placed in a heat treatment furnace at 1400°C, kept warm for 20 minutes, and then taken out and quenched with water.

[0035] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0036] The microstructure of the TiAl alloy after heat treatment in Example 1 is as follows: Figure 1 As shown in (a), it is mainly composed of white parent phase βo phase and gray lath martensite α2' phase. The sample was analyzed by EBSD, and the phase diagram analysis results are shown in Figure 1 As shown in (b), it can be seen that the content of martensite α2' reaches 96.9%, indicating that this heat treatment technology can produce a large amount of martensite.

[0037] The Vickers hardness of the martensitic TiAl alloy obtained in this Example 1 is shown in Table 1 below. The average value is 503.60 HV. The hardness range of ordinary TiAl alloys is roughly between 250 and 350 HV. This proves that the present invention not only obtains a TiAl alloy dominated by martensite and a preparation method thereof, but also that the obtained martensitic TiAl alloy has significantly improved mechanical properties, such as alloy hardness, compared with traditional TiAl alloys. Example 2

[0038] This embodiment aims to provide a martensitic TiAl alloy, i.e., a TiAl alloy containing relatively more martensite in its microstructure, and a preparation method thereof. The designed composition is as follows in terms of alloy atomic percentage: Ti-38Al-6.5V-2Zr, with the remainder being Ti and unavoidable impurities.

[0039] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for the smelting and casting of ingots are titanium sponge (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio to prepare a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for potential element losses during smelting.

[0040] Step (2) Melting the ingot The raw materials from step 1 were melted into button ingots in a vacuum arc melting furnace (VAR). The melting process was repeated five times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled within the range of 0.2kA to 0.3kA.

[0041] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0042] Step (4) Heat treatment The block sample was placed in a crucible and placed in a heat treatment furnace at 1350°C. After keeping the crucible for 30 minutes, it was taken out and quenched with water.

[0043] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0044] Figure 2 The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment in Example 2 of the present application is shown, which is mainly composed of a white parent phase βo phase and a gray martensite α2' phase. Software measurement shows that the content of martensite α2' reaches 83.10%. It can be said that it is mainly martensite, which meets the requirements of martensitic TiAl.

[0045] The alloy composition of this embodiment, combined with this heat treatment technique, still produces a predominantly martensite structure, achieving the invention's objectives. Furthermore, as shown in Example 1, holding at a higher temperature further promotes martensite formation and shortens the required holding time. As shown in Table 1 below, the average Vickers hardness of this martensitic TiAl alloy is 473.18 HV. While somewhat lower than the Vickers hardness in Example 1, it still represents a significant improvement over conventional TiAl alloys. This demonstrates that martensite formation increases alloy hardness and, on the other hand, indicates that reducing Al content reduces hardness, providing a reference for future alloy composition design. Example 3

[0046] This embodiment aims to provide a martensitic TiAl alloy, i.e., a TiAl alloy containing relatively more martensite in its microstructure, and a preparation method thereof. The designed composition is: Ti-42Al-6.5V-2Zr in terms of alloy atomic percentage, with the balance being Ti and unavoidable impurities.

[0047] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for the smelting and casting of ingots are titanium sponge (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio to prepare a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for potential element losses during smelting.

[0048] Step (2) Melting the ingot The raw materials from step 1 were melted into button ingots in a vacuum arc melting furnace (VAR). The melting process was repeated five times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled within the range of 0.2kA to 0.3kA.

[0049] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0050] Step (4) Heat treatment The block sample was placed in a crucible and placed in a heat treatment furnace at 1450°C. After keeping the temperature for 15 minutes, it was taken out and quenched with water.

[0051] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0052] Figure 3 The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment in Example 3 of the present application is shown, which is mainly composed of a white parent phase βo phase and a gray martensite α2' phase. Software measurement shows that the content of martensite α2' reaches 88.88%. It can be said that martensite is the main component, which meets the requirements of martensitic TiAl.

[0053] The alloy composition of this embodiment, combined with this heat treatment technique, still produces a predominantly martensite structure, achieving the invention's objectives. Furthermore, as shown in Example 1, maintaining the alloy at a lower temperature further promotes martensite formation. As shown in Table 1 below, the average Vickers hardness of this martensitic TiAl alloy is 544.10 HV, an increase over that of Example 1. This demonstrates that the formation of martensite increases alloy hardness and also suggests that higher temperatures are beneficial for increasing alloy hardness.

[0054] Comparative Example 1 This embodiment is a comparative example for the martensitic TiAl alloy and its preparation method in the above-mentioned embodiment 1. The atomic percentage of the TiAl alloy used in the experiment is: Ti-42Al-5.5V-3Zr, and the balance is Ti and unavoidable impurities.

[0055] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for smelting and casting ingots are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio and prepared into a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for possible element losses during smelting. Step (2) Melting the ingot The raw materials in step (1) were melted into button ingots using a vacuum arc melting furnace (VAR). The melting process was repeated 5 times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled in the range of 0.2kA to 0.3kA.

[0056] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0057] Step (4) Heat treatment The block sample was placed in a crucible, placed in a heat treatment furnace at 1400°C, kept warm for 20 minutes, and then taken out and quenched with water.

[0058] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0059] Figure 4 The scanning electron microscope (BSE-SEM) microstructure of the TiAl alloy after heat treatment in Comparative Example 1 of the present application is shown, wherein the white matrix is ​​the B2 phase, and the gray phase is the irregular Widmanstätten α2 phase. Software measurement shows that the content of Widmanstätten α2 reaches 86.7%, that is, Comparative Example 1 cannot obtain a martensitic TiAl alloy through the combined design of alloy composition and heat treatment.

[0060] The Widmanstätten microstructure obtained in Comparative Example 1 typically exists in a disordered β or α phase (HCP structure) at high temperatures (typically ≥1200°C). During rapid cooling (such as air cooling or pulsed current treatment), the α phase decomposes into lamellar structures of α2(Ti3Al) and γ(TiAl) through a non-equilibrium shear mechanism. This structure affects the material's mechanical properties, resulting in poor thermal stability and thermal stress corrosion resistance in high-temperature environments (such as aerospace applications). This comparative example provides a valuable reference for future martensitic TiAl alloy design, as shown in Table 1 below. The average Vickers hardness of this alloy is 490.02 HV, demonstrating that increasing Al and Zr content increases hardness.

[0061] Comparative Example 2 This comparative example is a comparison of the martensitic TiAl alloy and its preparation method in Example 1. The atomic percentage of the TiAl alloy used in the experiment is: Ti-42Al-4.5V-4Zr, with the remainder being Ti and unavoidable impurities.

[0062] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for smelting and casting ingots are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio and prepared into a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for possible element losses during smelting. Step (2) Melting the ingot The raw materials from step 1 were melted into button ingots in a vacuum arc melting furnace (VAR). The melting process was repeated five times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled within the range of 0.2kA to 0.3kA.

[0063] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0064] Step (4) Heat treatment The block sample was placed in a crucible, placed in a heat treatment furnace at 1400°C, kept warm for 20 minutes, and then taken out and quenched with water.

[0065] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0066] The microstructure of the TiAl alloy after heat treatment in Comparative Example 2 is as follows: Figure 5 As shown in (a), the white matrix is ​​the B2 phase, and the gray phase is an irregular lamellar Widmanstätten structure and a small amount of needle-shaped martensite, with a content of 86.7%. Figure 5 (b)

[0067] In other words, Comparative Example 2 did not produce a martensitic TiAl alloy. The resulting structure would affect the material's mechanical properties, resulting in a Widmanstätten TiAl alloy with poor thermal stability and thermal stress corrosion resistance in high-temperature environments (such as aerospace applications). As shown in Table 1 below, the average Vickers hardness of this alloy is 465.21 HV, demonstrating that the formation of both Widmanstätten and martensite structures improves the alloy's hardness.

[0068] Comparative Example 3 This comparative example is a comparison of the martensitic TiAl alloy and its preparation method in Example 1. The atomic percentage of the TiAl alloy used in the experiment is: Ti-42Al-8.5V, and the balance is Ti and unavoidable impurities.

[0069] The preparation of the TiAl alloy is achieved by the following steps: Step (1) Ingredients The raw materials used for smelting and casting ingots are sponge titanium (99.7 wt.%), high-purity aluminum particles (99.9 wt.%), high-purity vanadium particles (99.9 wt.%), and high-purity zirconium particles (99.8 wt.%). These materials are mixed uniformly according to the composition ratio and prepared into a 50g sample. To prevent large-scale volatilization of aluminum during smelting, an additional 3 wt.% of aluminum is added during the batching process to compensate for possible element losses during smelting. Step (2) Melting the ingot The raw materials from step 1 were melted into button ingots in a vacuum arc melting furnace (VAR). The melting process was repeated five times to obtain an ingot with uniform composition. The melting vacuum was less than 0.1 Pa, and the melting current was controlled within the range of 0.2kA to 0.3kA.

[0070] Step (3) Wire cutting Heat treatment samples were cut from the center of the ingot using a CNC wire cutting machine. The samples were in block shape and measured 8*8*8mm.

[0071] Step (4) Heat treatment The block sample was placed in a crucible, placed in a heat treatment furnace at 1400°C, kept warm for 20 minutes, and then taken out and quenched with water.

[0072] Step (5) Microstructure observation The sample was cut from the middle part and mechanically polished until the surface was mirror-finished and scratch-free. The structure was observed using a scanning electron microscope.

[0073] Figure 6 (a) shows the microstructure of the TiAl alloy after heat treatment in Comparative Example 3 of the present application, wherein the microstructure of the alloy is mainly composed of irregular Widmanstätten structure and a small amount of acicular martensite, with a total content of 96.9%. Figure 6 (b)

[0074] In other words, this comparative example failed to produce a martensitic TiAl alloy. The resulting structure compromises the material's mechanical properties, resulting in a Widmanstätten TiAl alloy with poor thermal stability and thermal stress corrosion resistance in high-temperature environments (such as aerospace applications). As shown in Table 1 below, the average Vickers hardness of this alloy is 447.01 HV, demonstrating that the formation of martensite increases the alloy's hardness, but increasing the V content decreases the hardness.

[0075] Table 1: Alloy composition, treatment methods and mechanical properties

[0076] By comparing Examples 1-3 with Comparative Examples 1-3, it can be seen that the present invention obtains a martensitic TiAl alloy with a predominantly martensitic structure through a combination of composition design and heat treatment process design. Overall, the alloy hardness, represented by Vickers hardness, is greatly improved compared to the hardness of traditional titanium aluminum alloys. In particular, martensitic alloy is a completely new TiAl alloy structure pattern. Although its full mechanical properties have not yet been tested due to the test period, its Vickers hardness alone is sufficient to deserve further attention and can at least be applied to the field of high-temperature alloys with high requirements, such as hardness and high-temperature performance.

[0077] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0078] The above description has been provided for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present disclosure to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A martensitic TiAl alloy, characterized in that: The martensite content in the TiAl alloy is more than 80%. The TiAl alloy contains, in atomic percentage, 38-43% Al, 6.5-8.5% V, 0.1-2% Zr, and the remainder is Ti and unavoidable impurities. The total atomic percentage of V and Zr is 8.

5.

2. The martensitic TiAl alloy according to claim 1, characterized in that The martensite content in the TiAl alloy is more than 85%. The TiAl alloy contains, in atomic percentage, 40-42% Al, 6.5-8.5% V, 0.1-2% Zr, and the balance is Ti and unavoidable impurities.

3. The martensitic TiAl alloy according to claim 1 or 2, characterized in that: The martensite content in the TiAl alloy is more than 90%. The TiAl alloy contains, in atomic percentage, 42% Al, 6.5% V, 2% Zr, and the balance is Ti and unavoidable impurities.

4. The martensitic TiAl alloy according to claim 1 or 2, characterized in that: The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1350-1450° C., keeping the ingot warm for 10-30 minutes, taking the ingot out, and quenching the ingot with water.

5. The martensitic TiAl alloy according to claim 4, characterized in that The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1380-1450° C., keeping the ingot warm for 20-30 minutes, then taking it out and quenching it with water.

6. The martensitic TiAl alloy according to claim 4 or 5, characterized in that: The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400-1450° C., keeping the ingot warm for 20-30 minutes, then taking it out and quenching it with water.

7. The martensitic TiAl alloy according to claim 4 or 5, characterized in that: The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400° C., keeping the ingot warm for 20 minutes, taking it out, and quenching it with water.

8. A method for preparing a martensitic TiAl alloy according to any one of claims 1 to 3, characterized in that: The steps include: Step 1: Ingredients The titanium sponge, high-purity aluminum particles, high-purity vanadium particles, and high-purity zirconium particles are uniformly mixed in the proportions described in any one of claims 1 to 3 to prepare a casting material to be used; Step 2: Melting ingots The casting material in step 1 is repeatedly melted multiple times in a vacuum arc melting furnace to obtain an ingot with uniform composition; Step 3: Cutting Cut the sample to be heat treated from the center of the ingot; Step 4: Heat treatment The sample to be heat-treated is placed in a heat treatment furnace at 1300-1450° C., kept warm for 10-30 minutes, and then taken out and quenched with water.

9. The method according to claim 8, characterized in that The TiAl alloy contains, in atomic percentage, 42% Al, 6.5% V, 2% Zr, and the balance being Ti and unavoidable impurities.

10. The method according to claim 8, characterized in that: The martensitic TiAl alloy is obtained by placing an ingot melted with a target composition in a heat treatment furnace at 1400° C., keeping the ingot warm for 20 minutes, taking it out, and quenching it with water.

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